The present invention relates to mine roof supports and particularly to supports which employ a goaf shield with a lemniscate guide system linking the goaf shield to the floor-engaging structure of the support.
In such supports, it is known to use a divided floor-engaging structure with a pair of spaced-apart skids which are able, independently of each other, to adjust themselves to uneven areas of the floor. A walking mechanism employing a hydraulic ram can be arranged in the gap between the floor skids. The walking mechanism usually comprises two resilient guide rods or bars with the shifting ram therebetween. The guide rods are connected at their ends nearest the mineral face with a head-piece attached to a longwall conveyor or to some other
It backing means. At the opposite goaf-side ends, the guide rods are connected to a guide element which moves along guides associated with the floor skids. German patent specification No. 25 40 091 describes a support of this known type. In this known construction, it is necessary to protect the walking mechanism between the floor skids; otherwise material from the rubble or goaf zone can penetrate the gap between the skids and disable the mechanism. For this purpose, a box can be connected to the goaf shield, as described in German patent specification No. 24 51 757. It is also known, in another aspect, i.e. for the purpose of protecting the main longwall working from the rubber or goaf zone, to provide a goaf screen which is composed of swivelling-suspended screen plates or the like, which overlap each other in the manner of fish-scales--see German patent specification No. 22 12 994.
In the case of the known lemniscate guided goaf shields with a walking mechanism arranged between the floor skids, the walking mechanism can become jammed between the floor skids despite the prevention of material from passing into the gap. During the outward thrust of the shifting ram, a moment is applied to the floor skids which tends to move the goaf-side ends of the skids towards each other and, in some circumstances, this leads to jamming or even blocking of the walking mechanism between the floor skids. Uneven areas of the floor aggravate the tendency of the floor skids to move towards each other at their goaf-side ends.
A general object of the present invention is to provide an improved roof support.